Berlin's startup culture is very international with employees from all around the world. Not really different to any other tech hub I know of. So English is the company's operating language, especially for global players like SoundCloud, Wooga, Ableton etc.. There are few companies in the tech sector who have German as their corporate language - and those mostly target the German market only.

There is a saying in the German startup-scene "Berlin Mitte is not a valid test market.". Berlin is the German capital but an outlier in almost every aspect.

No, only in multinationals.

Don't expect many people speaking English in small to middle size companies, nor in smaller cities.

yes, its common in Berlin for companies to use English. also the code is commented and documented in English.

if they have lots of foreigners and work for an international market, yes.